This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 10-2002-0082534 filed in Republic of Korea on Dec. 23, 2002, the entire contents of which are herein incorporated by reference.
1. Field of the Invention
The present invention relates to a multi-domain liquid crystal display (LCD) device and a method for manufacturing the same, and more particularly to a multi-domain LCD device and a method for manufacturing the same suitable for improving a peak transmittance.
2. Discussion of Related Art
With development of information society, demands for various display devices increase. Accordingly, much effort has been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent display (VFD). Some species of the flat display devices are already applied to displays of various equipments.
Among the various flat display devices, the liquid crystal display (LCD) device has been most widely used due to the advantageous characteristics of thinness, lightness in weight, and low power consumption, whereby the LCD device substitutes for a cathode ray tube (CRT). In addition to the mobile type LCD devices such as a display for a notebook computer, the LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in the LCD technology with applications in different fields, research in enhancing the picture quality of the LCD device has been in some respects lacking as compared to other features and advantages of the LCD device. In order to use the LCD device in various fields as a general display, the key to developing the LCD device lies on whether the LCD device can implement a high quality picture, such as high resolution and high luminance with a large-sized screen while still maintaining lightness in weight, thinness, and low power consumption.
Generally, an LCD device includes an LCD panel for displaying a picture image, and a driving part for applying a driving signal to the LCD panel. The LCD panel includes first and second glass substrates bonded to each other at a predetermined interval, and a liquid crystal layer injected between the first and second glass substrates.
The first glass substrate (TFT array substrate) includes a plurality of gate and data lines, a plurality of pixel electrodes, and a plurality of thin film transistors. At this time, the plurality of gate lines are formed on the first glass substrate at fixed intervals in one direction, and the plurality of data lines are formed at fixed intervals in perpendicular to the plurality of gate lines. Then, the plurality of pixel electrodes of a matrix arrangement are respectively formed in pixel regions defined by the plurality of gate and data lines crossing each other. The plurality of thin film transistors are switched according to signals of the gate lines for transmitting signals of the data lines to the respective pixel electrodes.
The second glass substrate (color filter substrate) includes a black matrix layer excluding light from regions except the pixel regions of the first substrate, R/G/B color filter layer displaying various colors, and a common electrode displaying the picture image. In case of an In-Plane Switching (IPS) mode LCD device, the common electrode is formed on the first glass substrate.
Next, a predetermined space is maintained between the first and second glass substrates by spacers, and the first and second substrates are bonded to each other by a sealant pattern having a liquid crystal injection inlet. At this time, the liquid crystal layer is formed according to a liquid crystal injection method, in which the liquid crystal injection inlet is dipped into a container having liquid crystal while maintaining a vacuum state in the predetermined space between the first and second glass substrates. That is, the liquid crystal is injected between the first and second substrates by an osmotic action. Then, the liquid crystal injection inlet is sealed with the sealant.
The LCD device is driven according to optical anisotropy and polarizability of liquid crystal. At this time, liquid crystal molecules are aligned with directional characteristics since the liquid crystal molecules respectively have long and thin shapes. In this respect, an electric field is applied to the liquid crystal for controlling the alignment direction of the liquid crystal molecules. That is, if the alignment direction of the liquid crystal molecules is controlled by the electric field, the light is polarized and changed by the optical anisotropy of the liquid crystal, thereby displaying the picture image.
The liquid crystal is classified into positive (+) type liquid crystal having positive dielectric anisotropy and negative (−) type liquid crystal having negative dielectric anisotropy according to electrical characteristics of the liquid crystal. In the positive (+) type liquid crystal, a longitudinal axis of a positive (+) liquid crystal molecule is in parallel to the electric field applied to the liquid crystal. Meanwhile, in the negative (−) type liquid crystal, a longitudinal axis of a negative (−) liquid crystal molecule is in perpendicular to the electric field applied to the liquid crystal.
FIG. 1 is an exploded perspective view illustrating some parts of a related art LCD device. As shown in FIG. 1, the related art LCD device includes lower and upper substrates 1 and 2 bonded to each other at a predetermined interval, and a liquid crystal layer 3 injected between the lower and upper substrates 1 and 2.
More specifically, the lower substrate 1 includes a plurality of gate lines 4, a plurality of data lines 5, a plurality of pixel electrodes 6, and a plurality of thin film transistors T. At this time, the plurality of gate lines 4 are formed on the lower substrate 1 in one direction at fixed intervals, and then the plurality of data lines 5 are formed in perpendicular to the plurality of gate lines 4 at fixed intervals, thereby defining a plurality of pixel regions P. Subsequently, the plurality of pixel electrodes 6 are respectively formed in the pixel regions P defined by the plurality of gate and data lines 4 and 5 crossing each other, and the plurality of thin film transistors T are respectively formed at crossing points of the plurality of gate and data lines 4 and 5. Also, the upper substrate 2 includes a black matrix layer 7 excluding light from regions except the pixel regions P, R/G/B color filter layer 8 for displaying various colors, and a common electrode 9 for displaying a picture image.
Herein, each thin film transistor T includes a gate electrode extending from the corresponding gate line 4, a gate insulating layer (not shown) on an entire surface of the lower substrate 1, an active layer on the gate insulating layer above the gate electrode, a source electrode protruding from the corresponding data line 5, and a drain electrode positioned opposite to the source electrode. Each pixel electrode 6 is formed of a transparent conductive metal having great light transmittance such as Indium-Tin-Oxide (ITO).
In the aforementioned LCD device, the liquid crystal layer 3 is aligned on the pixel electrode 6 by a signal applied from the thin film transistor T, and the light transmittance transmitting the liquid crystal layer 3 is controlled according to the alignment level of the liquid crystal layer 3, thereby displaying the picture image. The aforementioned LCD device drives the liquid crystal according to the electric field formed in perpendicular to the lower and upper substrates, in which transmissivity and aperture characteristics are great. Also, it is possible to prevent liquid crystal cells from being damaged due to static electricity in that the common electrode 9 of the upper substrate 2 serves as a ground.
Hereinafter, a related art multi-domain LCD device will be described with reference to the accompanying drawings.
FIG. 2 is a cross-sectional view illustrating a unit pixel of a related art multi-domain LCD device. As shown in FIG. 2, the related art multi-domain LCD device includes lower and upper substrates 21 and 22 being opposite to each other at a predetermined interval, and a liquid crystal layer 23 formed between the lower and upper substrates 21 and 22.
The lower substrate 21 includes a plurality of gate and data lines, a thin film transistor TFT, a passivation layer, a pixel electrode 24, and a first alignment layer 25. The plurality of gate and data lines crossing each other are formed on the lower substrate 21 to define a plurality of pixel regions. Also, the thin film transistor TFT having a gate electrode, a gate insulating layer, a semiconductor layer, an ohmic contact layer and source/drain electrodes is formed in the pixel region. Then, the passivation layer is formed on the entire surface of the lower substrate 21, and the pixel electrode 24 is formed on the passivation layer for being connected to the drain electrode. The first alignment layer 25 is formed on the entire surface of the lower substrate 21 including the pixel electrode 24.
The upper substrate 22 includes a black matrix layer 26 preventing light from leaking in the lower substrate 21 corresponding to the gate line, the data line and the thin film transistor, a color filter layer 27 formed on the entire surface of the upper substrate 22 including the black matrix layer 26, a common electrode 28 on the color filter layer 27, and a second alignment layer 29 on the common electrode 28.
Meanwhile, in the related art multi-domain LCD device, an opening 30 is formed in the color filter layer 27, thereby obtaining multi-domains. At this time, the opening 30 is formed when forming the color filter layer 27, and a VA mode is applied thereto, thereby forming a wide viewing angle.
However, the related art multi-domain LCD device has the following disadvantages. That is, the opening 30 is formed in the color filter layer of the upper substrate, whereby the opening may be asymmetrical by bonding margins of the lower and upper substrates. As a result, peak transmittance is unstable.